264 ON SOME N.S.W. TAN-SUBSTANCES. 



Decoction steeped in hide powder. 

 Filter. 



10 c.c. of the filtrate. 

 20 c.c. indigo. 



S 17*7 KMn0 4 required 1 st test. 



T 17-6 do. 2nd do. 



TJ 17-65 do. for lOc.c. filtrate- 16*9 = '75... V. 



*7-25 - -75 = 6-5 

 To bring it to the standard of 1 grm. to 1 litre, we have 6-5 = 1 '3 



.-. 9-8438 : 100 : : 1-3 :x 



x = 130 



= 13*206 % tannic acid. 



9.8438 



To find non-tannin, substitute '75 for 6*5, and we have 



1-524 % non-tannin. 



Particulars of Substance — Acacia salicina (bark), Tarella, 15th 

 August, 1887. 



Decoction made 15th August, 1888 ; examined for tannin, 16th 



August, 1888. 



We have now data on which to form results, but those results 

 must be presented with reference to a standard. It is usually 

 recommended to compare the amount of permanagate necessary 

 to oxidise the tannic acid in the bark, &c, with the quantity 

 required to oxidise the same weight of oxalic acid. But the chief 

 objection to this is the un desirability of comparing substances so 

 dissimilar as tannic and oxalic acids. 



Procter follows von Schroeder in substituting pure tannic acid 

 of oak-galls for oxalic acid, but, doubting that pure tannic acid 

 is readily obtainable, inclines to recommend oxalic acid, f which 

 is readily obtainable of uniform composition. Now Schering's 

 tannic acid is obtainable in the Colony, and not only has it a 

 high standard of purity, but it is fairly uniform. I have tried 

 both oxalic acid and tannic acid ; there is no practical difficulty 

 in the way of using the latter, ■ and the desirability of comparing 

 a tannic acid with a tannic acid is apparent. 



* The portion of the calculation which follows will be best understood 

 after the account of the standardisation of the permanganate, see p. 265. 



t He gives reasons (Journ. Soc. Chem. Ind., v,, 79) for substituting 

 gallic acid. 



